Furnace adapted for use in dilatometry



Ap 23, 1963 M. BRANCHEREAU ETAL 3,086,385

FURNACE ADAPTED FOR USE IN DILATOMETRY Filed Oct. 13, 1959 4 IN V ENTORS MAURICE BRANCHEREAU BY MAURICE NAVEZ United States Patent FURNACEADAPTER! :FGR USE IN BELATQMETRY Maurice Eranehereau, Vincennes, andMaurice Navez,

Paris, France, assignors to Iompagnie de Saint-Gotham,

Paris, France Filed Get. 13, 1959, Ser. No. 346,139 Claims priority,application France Get. 15, 1%8 15 Claims. ((Il. IS-16) It is necessary,in making precision dilatometry measurements, to have a furnace orheated enclosure in which the specimen being tested is introduced, whichis maintained at a precise temperature. A typical temperature at whichdilatometry measurements are made, for example, is 300 C. Suchtemperature must be maintained as uniform as possible, in order todecrease errors in measurement, particularly in the neighborhood of thecritical temperatures of the material of which the specimen is made.Finally, in order to be successful in an industrial laboratory, it isnecessary that the specimen be heated relatively rapidly to the desiredtemperature so that each measuring cycle, which includes alternatemeasurements on the heated and cooled specimen, may be relatively short.

Furnaces or ovens which are satisfactory for other purposes are notsatisfactory for the present purposes since they do not fulfill theabove requirements. As a matter of fact the introduction of a coldspecimen into the furnace at an elevated temperature causes largethermal perturbations which cause a relatively large gradient intemperature precisely in the region of the furnace where the temperatureshould be most uniform. As a result, the temperature of the specimencannot be brought to a value accurate enough to permit a correctmeasurement of the dilation or expansion of the specimen without anundue delay to achieve temperature equilibrium.

The present invention relates to an oven or furnace of the doublechamber type, which is characterized by the use of a first or outerheated chamber, and by a second heated chamber located interiorly of thefirst chamber and receiving the specimen to be heated. The externalchamber assures the maintenance of a chosen uniform temperature on itsinner surface, and the internal chamber, which is completely envelopedby the external chamber, has for its function the transmission of saidtemperature to the specimen to be heated.

Preferably both of the chambers, and in any event th external chamber,include a plurality of heating elements so constructed and arranged asto yield perfect uniformity in the temperature and the necessary heatinsulations. Such temperature is held accurately by control andregulating apparatus employed in conjunction with the furnace.

The specimen to be heated is supplied with heat from the system forheating the inner chamber, which is preferably placed in operation atthe moment of the introduction of the specimen into the apparatus.According to another manner of operation of the device of the inventionand to gain time said heating of the interior chamber may be startedbefore the introduction of the specimen, in such manner as to accumulatein advance a quantity of heat suflicient to produce all or a part of therise in tempera ture of the specimen which is required.

The present invention will be described in a detailed manner byreference to a preferred, non-limiting embodiment, of apparatus formaking precision dilatometric measurements. Such embodiment incorporatesa doublechamber furnace made in accordance with the present invention.It is clear that the furnace of the invention may be applied to otherapplications such as, for example, the determination of magneticpermeability as a function of temperature, or of Curie points. Thoseskilled in the art will, without difficulty, immediately comprehend aEfihiifid Patented Apr. 23, 1963 number of other uses to which thefurnace may be put.

In the accompanying drawings, forming a part of the specification:

FIG. 1 is a somewhat schematic view in vertical cross section throughthe aforesaid apparatus which makes precision dilatometric measurements;

FIG. 2 is a fragmentary view in said elevation on an enlarged scale ofthe lower end of the specimen holder; and

FIG. 3 is a view in transverse section through the specimen holder, thesection being taken along the line 33 of FIGS. 1 and 2.

Turning now to the drawings, the illustrated precision industrialdilatometer is of the vertical type, and has a microscopic head. Theapparatus includes a cold chamber, maintained at 0 C., and thedouble-chamber furnace of the present invention. The specimen beingtested is placed successively in the cold chamber and in thedoublechamber furnace, and the measurement of the elongation of thespecimen when heated to the temperature allows the determination of thelinear coefficient of dilation or expansion of the specimen.

in FIG. 1 the external chamber has its inner wall formed of an elongatedmetal tube 1 of great thickness which is preferably made of copper. Tube1 is provided with a number of discs or diaphragms 2, 2, preferably alsomade of copper, suitably distributed on both sides of central part 3that comprises no disc. At the upper end of tube 1 the discs 2 have acentral opening through which the specimen and its holder may beintroduced into the furnace. The bottom discs 2 and the upper pierceddiscs 2', taken two by two, form closed or partially closed spaces whichcontribute to the thermal equilibrium of the furnace. The discs 2 and 2'are made vertically adjustable with respect to tube 1, so that it ispossible to adjust the volume of the spaces between successive discs,whereby to obtain better thermal equilibrium of the furnace in certaincases.

Exteriorly of tube 1 there are placed heating coils for the externalchamber; in the embodiment shown such coils consist of a principalwinding 4, shown placed closer to tube l, and four auxiliary heatingcoils designated 5, 6, 7, and S, and shown disposed further from tube 1.It will be understood that the relative disposition of the principal andauxiliary heating coils may be varied as desired. The principal heatingcoil provides the major part of the necessary heat, and the fourauxiliary heating coils at their respective positions then provide localheat necessary to eliminate any gradient of temperature along the lengthof tube 1. The principal heating coil 4 is supplied with heating currentthrough its individual control means which may be in the nature of anauto-Variac. The auxiliary heating coils 5, 6, 7, and 8 are likewiseunder the control of their individual controlling elements 10, 11, 12and 13, which may be similar to element 9. Heating current for each ofthe heating elements is supplied from a suitable source 14 whichprovides a stabilized voltage. The tube 1 and the principal andauxiliary heating elements are enclosed within a heating insulatingchamber 15 which has a closed bottom and, closed sidewalls envelopingthe heating coils and tube 1, and a top having a central opening alignedwith the axis of tube 1.

By suitable adjustment of control means 9-13, inclusive, the furnace maybe heated to the desired temperature, and each temperature may be madeuniform throughout the total extent of the surfaces of the centralcavity 3 of the external chamber.

The interior chamber encloses a heating coil 16 which is disposed withincavity 3 extending about the axis thereof. Heating means 16 is sodisposed as to receive within it a specimen carrier 17 which extendsdownwardly into the furnace coaxial of tube 1. The specimen beingmeasured, designated 18, is disposed coaxial of specimen carrier 17, andthus lies coaxial of heating coil 16. The electric current necessary toheat coil 16 is furnished by an arrangement including an auto-Variac 19,which may be similar to devices 9- 13, inclusive, and a rheostat 20which is controlled by a regulator 21. Preferably regulator 21 is of thesocalled proportional action type, operated by a thermocouple having alarge variation of voltage with temperature change. The hot junction 22of such thermocouple is supported in the immediate neighborhood of thespecimen 18; the cold junction 23 of such thermocouple is maintainedvery accurately at 0 C. in an auxiliary enclosure designated 24.

Heating coil 16 furnishes all or the major part of the heat necessary toraise the specimen 18 and the specimen holder 17 to the desiredtemperature. The heating of coil 16 decreases or ceases when thespecimen attains the desired predetermined elevated temperature at whichthe measurement is to be made. Heating coil 16 functions to regulate thetemperature of the furnace during such measurement so that it is notnecessary, during such measurement, to vary the heating of coils 4, 5,6, 7 and 8 of the external chamber. Thus the current supplied to suchlatter coils may be initially determined, and need not be further variedthroughout a series of measurements.

The specimen 18 is positioned at the bottom of the tubular specimenholder 17, the latter being closed at its lower end. The upper end ofthe specimen holder is supported, by means not shown, under amicroscopic head 25 of apparatus which measures changes in length. Thespecimen 18 is in contact with a longitudinally-extending rod 26 whichis of very accurate length and diameter and which slides freely in thespecimen holder 17. The upper end of rod 26 engages the feeler of themicroscopic head 25. In order to minimize the values of residualcorrections, the specimen holder 17 and the rod 26 are made of the samematerial, and preferably are made of material having a low coefficientof expansion such as, for example, transpanent silica.

The construction of the specimen holder 17 is shown more fully in FIGS.2 and 3. The side wall of the specimen holder is provided with threevertical slots or windows 27 equally spaced 120 apart. Slots 27 allowthe three hot junctions 28 of three thermocouples to be placed directlyin contact with the surface of the specimen 18. Preferably one of suchjunctions engages the top of the specimen, the second engages generallythe midst of the specimen, and the third engages the bottom of thespecimen.

The cold junctions 29 of such three thermocouples are immersed in a bathcontained in the auxiliary enclosure 2.4 and accurately held at 0 C.Such three thermocouples are preferably of the platinum-platinum rhodiumalloy type (10% rhodium, 90% platinum). The auxiliary enclosure 24contains a liquid 31 in which are immersed the cold junctions 23 and 29'which is a good conductor of heat and has good dielectric orelectrically insulating properties. The bath is maintained at uniform 0temperature and is stirred by an agitator or propeller 3'1 driven by amotor 32. The auxiliary container 24 is immersed throughout asubstantial part of its depth in melting ice and water bath 33 whereinthe temperature is maintained substantially constant by manual agitatorsas shown.

Measurement of temperature by means of the three thermocouples iscarried out very accurately by means of a potentiometer 34, sensitive tothe microvolt, which may be connected sequentially to the respectivethermocouples by the switch 35. When an accurate instrument 34 isemployed the temperature of each point on the sample may be obtainedwith an accuracy of i0.1 C. The fourth position of switch 35', which isthat shown in FIG. 1, allows the three thermocouples to be connected inseries, the series connected thermocouples being then connected to thepotentiometer 3 3. This gives a reading on potentiometer 34 which is thesum of the three thermoelectric forces, and determines the meantemperature of the specimen 18 with a high degree of precision. Theapparatus thus insures that the error difference between each of thelocal temperatures and the mean temperature of the specimen shall notexceed a predetermined value.

The dilatometer includes, in addition to the heated chamber or furnaceand its accessories which have been described above, a cold chamber ofthe type used in the International Bureau of Weights and Measures, suchcold chamber being maintained very accurately at a temperature of 0 C.In accordance with one particularly advantageous embodiment, the coldchamber and the heated chamber may be placed upon a support whichrotates in such manner that the axis of each of the enclosures may bemoved to coincide with the axis of the specimen holder. Such support mayalso be adjusted to the desired height, as for instance by an oil press.With such arrangement, the axis of the specimen holder with itscontained specimen may be placed in alignment with the axis or" theconsidered chamber and may be successively introduced into the coldchamber and then into the heated chamber by progressively raising thesupport. In making measurements with the apparatus above described andshown in the drawings, the temperature of the furnace or oven is firstregulated by proper adjustment of the voltages to which the heatingcoils 4-8, inclusive, are subjected. The principal heating element isenergized to give a temperature below that desired. The inevitablegradient in temperature at the interior of the external chamber is thencorrected by placing in service the four auxiliary heating elements 5-3,inclusive. Such auxiliary heating elements are energized in such manneras to obtain a uniform temperature longitudinally of the cavity 3. Suchadjustment of the auxiliary heating elements may be made with the aid ofsuitable thermocouples (not shown) disposed temporarily into such cavity3.

The specimen 18, whose length is measured by the microscopic head 25, issuccessively cooled to 0 C. by the cold bath and is then heated to thedesired temperature in the furnace. At the moment when the specimenholder is thrust into the interior of the furnace the regulatingthermocouple aflixed to the specimen holder will be placed in thefurnace at the same time and will operate the regulating heating element16 which is thus placed in operation and compensates for the cooling ofcavity 3 caused by the introduction of the cold specimen. At the sametime the final temperature of the specimen is attained, and ismaintained uniform throughout the time necessary for the dilationmeasurement.

According to an alternative embodiment, in order to shorten the timerequired for making such measurement the regulating heating element 16may be energized before the introduction of the specimen into cavity 3,and may thus participate in the initial heating of the furnace, causingthe temperature of cavity 3 to rise above the final predeterminedtemperature desired. The introduction of the cold specimen holder andthe cold specimen will then decrease the temperature of the furnace tothe desired temperature, and the regulating thermocouple and heat coil16 will assure the stabilization of such temperature.

The above described dilatometer permits the deter mination of thecoetlicient of linear dilation or expansion for a large number of solidsubstances and in a variety of forms.

By way of example the described apparatus permits the obtaining of atemperature gradient less than 0.3 C. from one extremity to the other ofa specimen having a length of mm., and to determine the mean temperatureof the specimen with an accuracy better than i0.2 C. When a microscopichead sensitive to the tenth of 0. micron is employed, the accuracy ofsuch apparatus is at least comparable or equal to that of existinginterferential dilatometers. With specimens of standard known lengths,the coefficients of dilation may be obtained in absolute values.Measurements may be made with the apparatus with great rapidity; forexample, in one hour with an apparatus provided with one microscopichead a complete measurement may be carried out. Alternatively, 12determinations of coefificients of dilation may be made in 8 hours withan apparatus embodying two heads so as to permit simultaneousmeasurements on two specimens at one time with the same equipment, inthe manner outlined above wherein cold and heating chambers are disposedon the same rotatable support.

Although only a limited number of embodiments of the invention have beenillustrated in the accompanying drawings and described in the foregoingspecification, it is to be expressly understood that various changes,such as in the relative dimensions in the parts, materials used, and thelike as well as the suggested manner of use of the apparatus of theinvention, may be made therein without departing from the spirit andscope of the invention as will now be apparent to those skilled in theart.

What is claimed is:

1. A furnace comprising a first, internal heating chamber adapted toreceive an object to be heated, heating means for said first chamber, asecond, external heating chamber containing the first chamber, heatingmeans within said second chamber and outside said first chamber of theelectrical resistance type comprising a principal heating coil extendingthroughout substantially the entire length of the second chamber andsupplying the major part of the necessary heat energy, and auxiliarywindings located at different localized zones within the second chambersupplying additional heat at said various localized zones, said secondchamber heating means maintaining the internal surface of the secondchamber at a predetermined desired temperature, the first chambertransmitting the necessary heat to said object to heat the same to apredetermined temperature.

2. A furnace as defined in claim 1 wherein said internal chamber haspositioned at each end thereof a plurality of temperature stabilizingzones formed by a plurality of spaced-apart partitions supported by theexterior wall of said chamber, and wherein the internal chamber heatingmeans is positioned in the central part of said chamber.

3. A furnace as defined in claim 2 wherein said partitions are movabletoward and away from each other along the axis of said internal chamberwhereby the volume included between successive partitions may be varied.

4. A furnace according to claim 1 in which the heating means inside theinternal chamber is of the electrical resistance type and comprises aheating coil positioned for surrounding the object to be heated andcontrol means for regulating the temperature of the object to keep thesame constant during the whole time it is maintained in the furnace.

5. A furnace according to claim 4 in which the control means for theheating coil of the internal chamber is actuated before the introductionof the object and its action is suppressed when the object is brought tothe desired temperature.

6. A furnace according to claim 4 in which the control means for theheating coil of the internal chamber is actuated when the object isintroduced in said chamber and its action is suppressed when the objectis brought to the desired temperature.

7. A furnace according to claim 6 wherein the control means for theheating coil of the internal chamber comprises a regulator operated by athermocouple having its hot junction placed in the immediateneighborhood of the object.

8. A furnace according to claim 4 in which the heating coil is placed inthe central part of the internal chamber between an upper and a lowerzone provided with parallel transverse partitions supported by theexterior wall of said chamber, the partitions of the upper zone leavinga central opening for the reception of the object to be heated.

9. A furnace according to claim 8 in which the distance between thepartitions is adjustable.

10. A furnace adapted for use in a precision dilatometer comprising afirst, internal heating chamber having an opening therein adapted toreceive a specimen holder, a second, external heating chamber containingthe first chamber, and heating means within the second chamber andoutside the first chamber, said heating means maintaining the internalsurface of the second chamber at a predetermined temperature, the firstchamber transmitting said predetermined desired temperature to theobject to be heated, said heating means comprising a first heatingresistance coil surrounding substantially the entire partitionseparating the internal chamber from the external chamber and aplurality of auxiliary heating coils acting on localized parts of theheight of the external chamber and being separately regulated forcompensating the temperature differences which may be established alongthe height of the external chamber.

11. A precision dilatometer comprising a specimen holder, a microscopichead for the specimen holder, and a furnace for heating the specimenholder and the contained specimen to the predetermined desiredtemperature, said furnace comprising a first, internal heating chamberhaving an opening therein adapted to receive the specimen holder, asecond, external heating chamber containing the first chamber, andheating means within the second chamber and outside the first chamber,said heating means maintaining the internal surface of the secondchamber at a predetermined temperature, the first chamber transmittingsaid predetermined desired temperature to the object to be heated, saidheating means comprising a first heating resistance coil surroundingsubstantially the entire partition separating the internal chamber fromthe external chamber and a plurality of auxiliary heating coils actingon localized parts of the height of the external chamber and beingseparately regulated for compensating the temperature differences whichmay be established along the height of the external chamber.

12. A precision dilatometer as defined in claim 11 in which the specimenis contained in a specimen holder whose side walls is provided withthree slots equally spaced of permitting the direct contact of the hotjunctions of thermocouples with the surface of the specimen.

13. A precision dilatometer as defined in claim 11 in which means areprovided for placing the axis of the specimen holder in alignment withthe axis of the heated chamber.

14. A precision dilatometer as defined in claim 13 in which the specimenholder is raised by a support so that it may be successively introducedin the heated and into a cold chamber.

15. A furnace adapted for use in a precision dilatometer comprising afirst heating chamber having an opening therein adapted to receive aspecimen, a second heating chamber surrounding said first chamber,heating means within said second chamber whereby the internal surface ofthe second chamber is maintained at a predetermined temperature andcomprising a first heating resistance coil surrounding substantially theentire partition separating the first chamber from the second chamberand a plurality of auxiliary heating coils acting on localized parts ofthe height of the second chamber and being separately regulated forcompensating the temperature differences which may be established alongthe height of the external chamber, heating means for said firstchamber, control means for said first chamber heating means comprising aregulator operated by a thermocouple which has its hot junc- ReferencesCited in the file of this patent UNITED STATES PATENTS Wales "June 27,1939 Kingston June 13, 1944 Jung June 24, 194

Miller Mar. 23, 1948 Lubin Ian. 31, 1950 Peckham July 10, 1951 Rich eta1 May 6, 1952 Font May 7, 1957 Craiglow et a1 Feb 28, 1961

11. A PRECISION DILATOMETER COMPRISING A SPECIMEN HOLDER, A MICROSCOPICHEAD FOR THE SPECIMEN HOLDER, AND A FURNACE FOR HEATING THE SPECIMENHOLDER AND THE CONTAINED SPECIMEN TO THE PREDETERMINED DESIREDTEMPERATURE, SAID FURNACE COMPRISING A FIRST, INTERNAL HEATING CHAMBERHAVING AN OPENING THEREIN ADAPTED TO RECEIVE THE SPECIMEN HOLDER, ASECOND, EXTERNAL HEATING CHAMBER CONTAINING THE FIRST CHAMBER, ANDHEATING MEANS WITHIN THE SECOND CHAMBER AND OUTSIDE THE FIRST CHAMBER,SAID HEATING MEANS MAINTAINING THE INTERNAL SURFACE OF THE SECONDCHAMBER AT A PREDETERMINED TEMPERATURE, THE FIRST CHAMBER TRANSMITTINGSAID PREDETERMINED DESIRED TEMPERATURE TO THE OBJECT TO BE HEATED, SAIDHEATING MEANS COMPRISING A FIRST HEATING RESISTANCE COIL SURROUNDINGSUBSTANTIALLY THE ENTIRE PARTITION SEPARATING THE INTERNAL CHAMBER FROMTHE EXTERNAL CHAMBER AND A PLURALITY OF AUXILIARY HEATING COILS ACTINGON LOCALIZED PARTS OF THE HEIGHT OF